<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>续</title>
    <style>
        body>div{
            width: 200px;
            height :200px;
            background-color:red;
        }
        div>div{
            width:50px; height:50px;background-color:green;
            margin-left:20px;
            /*当元素的边缘和上级元素的边缘时重叠时
            给元素加上边距胡出现粘连问题,给上级元素添加
            overflow:hidden
            */
            margin-top:50px;

        }
        h1{
            margin:0 0 10px 0;/*修改原有上下边距*/
        }
        p{
            margin-top:0;/*去掉自带的外边距*/
        }
        ul{
            margin-top: 10px;
        }

    </style>

</head>
<body>
<div>
    <div></div>
</div>

<h1>这是h1</h1>
<p>这是p</p>
<ul>
    <li>aaa</li>
    <li>bbb</li>
    <li>ccc</li>
</ul>


</body>
</html>